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The Lonely Star of Autumn

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Darrell Heath-Astronomy columnist

As we enter into autumn
we bid a fond farewell
to the constellations of
summer such as Cygnus,
Hercules, Scorpius and
Sagittarius and say hello to
a few new arrivals.
To the north and northeast
we have Cassiopeia,
Perseus, Pegasus, Andromeda,
and Aries and to the
south we have a group of
star patterns with a water
theme to them like Aquarius,
Pisces, and Cetus.
And right below Aquarius
there is another fishy
constellation, Piscis Austrinus
(the southern fish).
In fact, in most artist representations
Aquarius is
pouring water from a jug
into the southern fish’s
open mouth.
There is another common
element to these watery
constellations of our
southern sky: they are all
dim and hard to see.
However there is one
star among them that really
does stand out, its
name is Fomalhaut and
it is the alpha star (the
brightest visible star) in
the constellation of Piscis
Austrinus.
You can pronounce
“Fomalhaut” in one of two
ways: “FOAM-ah-low” or
Foam-a-lot.”
Facing south on late autumn
evenings you will see
it low along the horizon
and shining nicely as our
18th brightest star.
The name “Fomalhaut”
means something along
the lines of “the mouth of
the fish” and is an Arabic
translation of the description
that the last of the
great Greek astronomers,
Ptolemy, had given it.
While the translation
of “Fomalhaut” may be
“the mouth of the fish” we
amateur astronomers have
a special nickname for it:
“The Lonely One”, or “The
Lonely Star of Autumn.”
We give it this moniker
because, without any other
bright stars in the nearby
vicinity, it just seems so
all-alone.
But appearances can
be deceiving and as we
shall see in just a moment,
Fomalhaut is not quite as
lonely as it seems.
Fomalhaut is about 25
light years away, is twice
the size of our own Sun,
and some 17 times as
bright.
It’s also very hot. The
darrell heathhas a toasty surface
temperature of around
10,000 degrees Fahrenheit
but Fomalhaut is a much
warmer 15,000 degrees
Fahrenheit. It’s also a fairly
young star at 440 million
years of age.
That’s old to you and
me but in terms of the
lifespans of the average
star Fomalhaut is just a
pup. But there is an important
caveat to add here:
hot, massive stars live fast
and die young and since
Fomalhaut has twice the
mass of our Sun its total
life expectancy is figured
to only be about a billion
years or so.
The Sun’s total life expectancy
is around 11 billion
years so both it and
Fomalhaut are actually
middle aged.
Now, if that nickname
of “The Lonely Star” has
you feeling all weepy for
Fomalhaut you can put
aside the tissues because
it just isn’t so.
We now know that Fomalhaut
has a couple of other
stellar companions. One
is an orange-colored dwarf
star (Fomalhaut B) about
1 light year away from the
primary and the other is a
red dwarf star (Fomalhaut
C), the most common type
of star in the universe, located
some 2.5 light years
from Fomalhaut A.
These are very wide
separations for multiple
star systems and it made
things a bit tough for astronomers
to get the data
they needed to confirm
that the stars are indeed
gravitationally connected
with each other.
But wait, there’s more!
We’ve known for some
time that Fomalhaut is surrounded
by a disk of gas,
dust, and ice (making it
look like the Eye of Sauron
from Tolkien’s The Lord of
the Rings), the stuff that
planets are formed out of,
and in 2008 astronomers
announced that they had
found an exoplanet candidate
amidst the debris
disks.
Designated Fomalhaut
b (astronomers use lower
case letters for planet designations
and upper case
letters for the parent star)
this alien exoplanet became
the first ever world
outside our own solar system
to be imaged directly
by photographic means.
The planet is still
shrouded in dust and may
be as massive as our own
Neptune or it could contain
three times the mass of
Jupiter.
It also has a rather
weird, highly elliptical orbit
that takes the planet
on a 1,700 Earth-year long
trip around its parent star!
That’s a long year by anyone’s
standards.
Another study from a
few years back says that
the disk contains billions
to tens of trillions of cometlike
bodies and that their
constant collisions with
one another helps to keep
the disk supplied with
fresh dust material.
Not to be outdone, it
was announced last year
that a small debris disk
also surrounds Fomalhaut
C.
We don’t know yet
whether or not there is
anything planet-like within
this disk but we do know
one thing for certain: Fomalhaut
is not so lonely after
all and it still continues to
surprise us.